The major objective of this grant is to identify, characterize and determine the mechanism of action of the oncornaviral protein(s) involved in the malignant transformation of normal cells by oncogenic C-type viruses. We have previously published a series of papers that describe the mechanism of synthesis of Rauscher murine leukemia viral proteins. We have extended these studies to Moloney murine leukemia viruses and Moloney murine sarcoma viruses and their infected cells. We are in the process of studying the steps involved in the synthesis and processing of these virus specified proteins. We have at our disposal two murine sarcoma virus mutants that are temperature sensitive for the transformed phenotype. Viral precursor proteins and mature proteins are being characterized immunologically by use of various monospecific and polyspecific antisera prepared against murine leukemia and murine sarcoma virus proteins. The various viral proteins will be further characterized by peptide mapping to determine precursor-product relationships. Tumors have been produced in rats by injection of murine sarcoma virus-induced rat bone tumor cells into NZB rats. Sera from such animals immunoprecipitate several interesting polypeptides from sarcoma virus transformed cells that are not found in untransformed, leukemia virus infected cells. One particular size class (approximately 32,000 daltons) is not immunoprecipitated by antisera to disrupted murine leukemia or sarcoma virus or by antisera to p30 or gp69/71. This protein is found in mouse, rat, and cat cells transformed by Moloney murine sarcoma virus. The nature of this protein and others is under active investigation. In an attempt to assess the biological activity of potential 'src' gene products, we have acquired equipment required to perform micro-injecton experiments with single animal cells. We plan to purify candidate 'src' gene product(s) and test their effects by microinjection, a very demanding technique.